1. Field of the Invention
The invention relates to a process for selectively recovering thermoplastic polymers, and particularly polyester polymers from collections of yarns, films, fibers or fabrics, including dyed polyester fibers, for use in production of new undyed thermoplastic products, particularly polyester fibers, films and the like. More specifically, the invention relates to a process for selectively recovering polyester polymer by means of stripping the dye from dyed polyester fibers, subsequently dissolving the polyester fibers, separating the solution from any insoluble materials, and thereafter recoverying the polymer, without precipitation thereof, by evaporation of the solvent from the molten polymer.
2. Prior Art
The consumption of thermoplastic polymers is greater than ten billion pounds per year. Some, such as polyethylene, polypropylene, polyvinylchloride, polystyrene, polyamides and polyester, surpass the billion pounds per year rate. The use of many of these relatively expensive thermoplastic polymers for synthetic fibers has, notwithstanding significant periods of decline, increased tremendously.
Concomitantly the world is facing a shortage of raw materials for thermoplastic polymers; and sophisticated and efficient methods of recycling are needed.
Various methods have been described in the prior art for separation and/or recovery of thermoplastic polymer, including polyester polymers, from scrap polymers; and these have included the dissolution of the polymer in various solvents; thereafter precipitating and recovering the polymer. The objects of such processes were to avoid polymer degradation and/or to separate from the usable polymer the degraded polymer and/or monomers as impurities. The processes were slow and expensive; suitable only for laboratory usage; and they neither addressed themselves to nor did they solve fiber separation and dye removal problems.
Our copending U.S. patent application Ser. No. 578,592 filed May 19, 1975, now U.S. Pat. No. 4,003,850, discloses a process for recoverying polyester from waste fabrics or fibers by dye stripping, selectively dissolving the polyester fibers, removing the undissolved fibers and any other undissolved impurities from the solution; and thereafter precipitating polyester out of, and separating the polyester from the solution.
Whether by prior art processes or by the copending process described, the precipitation of polyester out of solution inevitability brings forth with the precipitated polyester polymer substantial quantities of the solvent and dye which must be separated from the newly precipitated polymer by way of decantation and/or filtration (for gross separation) as well as evaporation or solvent leaching or washing (for trace removal). Since the precipitation step does not eliminate the necessity for evaporation or equivalent treatment, and complicates rather than simplifies dye removal, it will be seen that elimination of the precipitation step in an efficient method of separating the polyester polymer from the solvent would be a meritorious advance in the art, and constitutes a primary object of this invention.
It is another advantage of this invention that the same solvent or solvent system may be used for both dye-stripping and polymer recovery, as well as for fiber separation.
It is also an advantage of this invention that removal of solvent from recovered polyester is greatly simplified and that solvent removal may be conveniently combined with a polymerization step wherever needed to increase molecular weight.